1. Field of the Invention
The invention relates to a digital multimeter, and particularly to a digital multimeter that realizes automatic selection of multiple categories of analog amount measurement functions and measuring ranges based on measured objects, using a voltmeter consisting of a fast analog/digital converter as the core, together with a proper auxiliary power supply, microprocessor, and electronic switches.
2. Description of the Related Art
Common digital multimeters generally provide mechanical or button-type function selection switches for users to judge and select measurements, themselves. For example, with regards to whether a measured object provides DC/AC voltage, resistance, or DC/AC current, the knob switch is turned to the corresponding function measurement position and some electrical connections are generated by metal contacts to form certain measurement circuits corresponding to the DC/AC voltage, resistance, or current measurements. Digital multimeters with an automatic measuring range can, after selecting a measurement function, select a proper measuring range using different combinations of internal electronic positions in accordance with the size of the measured object. Therefore, digital multimeters can complete measurements that yield measured values of different sizes (e.g., DC voltage) after only one position is selected for the measurement function (e.g., DC voltage). Multimeters with a manual measuring range require that the user select one of several positions appropriate for measuring a certain measurement function if the measurement value falls within the measurement scope (e.g., DC voltage). No existing multimeter can select all measurement functions automatically.
Designs have been described which add the automatic selection of the measurement function based on a digital multimeter with automatic measuring ranges. However, a signal-type detector is generally required to detect the type of analog input signal. The types of analog input signal that can be detected for this purpose are limited. Moreover, the influences of the input impedance and switches in signal-type detectors reduce the performance of multimeters with automatic selection of measurement functions, even giving them little practical value.
A considerable improvement has been made for multimeters with automatic selection of measurement functions in China patent number 200310112175.3, bringing the multimeter with automatic selection of measurement functions into practical use. However, in terms of the automatic selection of non-voltage/current passive analog input, great limits remain, such as for the measurement of capacitance, inductance, and diode voltage.
An objective of the invention is to provide a new type of digital multimeter with an automatic measuring range selection function, which not only can automatically select the measurement function based on whether the measured object provides DC/AC voltage, resistance, or DC current, but which has the feature of automatically selecting the measurement function among more types of passive components, including resistance, such as measurements of resistance, capacitance, inductance, and diode voltage. Under the simplest conditions, the ON/OFF functionality of this multimeter can be performed only by the ON/OFF switch of a power supply. Moreover, this multimeter has a response speed that is faster than that of common multimeters that automatically detect measurement ranges during measurements.